1. Technical Field
The present invention relates to a butt welding apparatus and a butt welding method for melting and joining a butt portion obtained by butting end faces of at least one plate member to be welded to each other with electric resistance heat generated by supplying power between a pair of electrode members.
2. Background Art
JP2003-305572A describes a butt welding apparatus where a pair of electrode members are arranged at a butt portion formed by butting end faces of two plate members to be welded to each other and the butt portion is melted and joined with electric resistance heat generated by applying power between the electrode members.
The conventional butt welding apparatus is a butt welding apparatus having a pair of electrode members disposed on both sides of two plate members to be welded in a thickness direction thereof, end faces of the two plate members being butted to each other to constitute a butt portion and each of the electrode members having such a thickness as to bridge across the butt portion, for melting the butt portion of the two plate members to be welded with electric resistance heat generated by supplying current between the electrode members to join the plate members to be welded, where press portions are provided in the pair of electrode members, for pressing one plate member of the two plate members to be welded in the thickness direction thereof to swell and deform the end face of the one plate member to be welded, which faces the other plate member to be welded, toward the other plate member to be welded according to this pressing.
According to the conventional butt welding apparatus, one plate member of two plate members, namely, one side portion of both side portions of the butt portion, is pressed by the pressing portions of the pair of electrode members at a starting time of a butt welding work. Thereby, the end face of the one plate member which faces the other plate member, in other words, the end face on the one side portion which faces the opposite side portion swells and deforms toward the opposite side portion to come in contact with the end face of the one side portion securely. Therefore, even if the end faces of these portions are not subjected to polishing work or the like for finishing prior to a butt welding work, an electrically conductive state between the end faces of the both portions can be ensured and a nugget bridging across these end faces is securely formed so that a large joining strength can be achieved.
Further, in the conventional common butt welding where a pair of electrode members are used, foils comprising metal thin films bridging across a butt portion of plate members are placed on both surfaces of the plate members in a thickness direction thereof, and a pair of electrode members are brought in pressure contact with the plate members via these foils so that a butt welding of the plate members is performed while preventing melding pieces generated due to electric resistance heat from leaking externally. However, according to the conventional butt welding apparatus described in JP2003-305572A, such foils are made unnecessary.
Furthermore, according to the conventional butt welding apparatus, when both side portions of the butt portion are different in thickness or when they have the same thickness, at least one electrode member of the pair of electrode members is formed in a shape of a projecting stepped portion so that the one side portion of both side portions of the butt portion can be pressed toward the thickness direction of the plate members. As a result, the end face of the one side portion is caused to swell and deform toward the opposite side portion of both side portions and, therefore, the end faces of the plate members positioned at both side portions can be brought in contact with each other.
In the conventional butting welding apparatus, however, the projecting amount of the projecting stepped portion provided on the at least one electrode member of the pair of electrode members is set according to the thickness sizes of both portions of the butt portion to be butt-welded. Therefore, when butt welding works are performed on respective plate members having differences in thickness between both side portions of their butt portions or when butt welding work is performed on a plate member having the same thickness size of both side portions of a butt portion thereof, electrode members which are respectively provided with projection portions having different projecting amounts are eventually used. Accordingly, various electrode members provided with projecting stepped portions having different projecting amounts must be prepared in order to allow each of the plate members having various thickness sizes of both side portions of the butt portion to be butt-welded.
An object of the present invention is to provide a butt welding apparatus and a butt welding method where end faces of at least one plate member to be welded are butted to each other, and butting welding works regarding respective plate members to be welded having various thickness sizes of both side portions of their butt portions can be implemented by electrode members made common.